A novel self-branching MnCo₂O₄/ nanographene hybrid composites on macroporous electrically conductive network as bifunctional electrodes for boosting miniature supercapacitors and sodium ion batteries

In situ construction of 3D MnCo₂O₄/graphene composites on a porous framework is a desirable means to improve charge storage and cycling lifetime of energy storage devices. Herein, a bifunctional MnCo₂O₄/nanographene hybrid composites (B-n-MnCo₂O₄) with novel self-branching construct are prepared on a macroporous electrically conductive network (MECN) for boosting miniature super-capacitors and sodium ion batteries. The porous B-n-MnCo₂O₄@MECN electrode provides adequate space to accommodate the large volume change and structural expansion during cycling. As a result, the 1 cm² electrode boasts a capacitance of ∼7.02 F cm⁻²/∼2341 F g⁻¹ at 3 mA cm⁻². The B-n-MnCo₂O₄@MECN||AC@Ni-foam supercapacitor with a high energy density (32.0 Wh kg⁻¹, at 6400 W kg⁻¹) has a long lifetime as manifested by only 20% capacitance deterioration after 20,000 cycles. Meanwhile, as an anode in sodium-ion batteries (SIBs), B-n-MnCo₂O₄@MECN has a reversible specific capacity of 541.2 mAh g⁻¹ at 50 mA g⁻¹ and rate capability of 150.0 mAh g⁻¹ at 200 mA g⁻¹. Nanographene not only provides the conductive network for the self-branching MnCo₂O₄ to accelerate electron conductivity and ion transport, but also relieves the volume changes during cycling. The strategy and bifunctional materials have a large potential in different types of energy storage devices.